Flavour as a Reading

On a homogeneous space M = Sp(2n,R)/U(n) carrying a compact group action, a kinematic no-go establishes that no quantity derivable from the manifold, the metric, the base point and the group can label the members of a certain triple. This paper measures in the layer that premise does not reach: the layer in which a clock and a system are separated and one is conditioned on the other. The central result is structural — the triple and the clock are one consequence, not two. A single input, an irreducible of the compact group occurring with multiplicity m, forces at once that the sector is Sym2(Cm), that the commutant is u(m), and that the available clock is the Cartan of su(m) inside it, of dimension m−1. At m = 2: three lines, a four-dimensional commutant, a torus of rank two, a clock unique up to scale, weights {+1, 0,−1}. At m = 1: one line and no clock at all, measured in the same block, as the arena’s own falsifier. The clock is not assumed periodic; its compactness and minimal period are measured, and its overlap function, its three orthogonal readings and its sensitivity to the clock-state phase freedom follow in closed form from covariant-POVM formulae. With a distinguished tangent direction admitted, one exact measurement lifts the degeneracy: the projection of the adjoint square, restricted to the sector, is exactly diagonalwith integer equispaced spectrum. Two limitation theorems then show that admitting the direction buys classes but not one invariant direction, and that no spectral invariant can supply the one remaining bit. A family index is therefore a reading: the value a line takes on a clock derived from the same multiplicity that produced the line, with a residual bit gauge-fixed relative to an orientation the construction does not supply.